Generally, present-day television receivers have a cathode ray tube display system with a deflection angle of about 90.degree. . Such display systems frequently employ a saturable reactor of the "E" core type to effect correction of side pin-cushion distortion. Moreover, the known saturable reactors utilized in such systems are of the "E" core type having three leg members with a substantially equal air gap in each one of the leg members.
When the leg members have equal air gaps a control winding may be affixed to either the outer or the center leg members with an impedance winding affixed to the unused leg members. In one known form of prior art structure a control winding is affixed to the outer leg members and a substantially parabolic-shaped waveform of current at the vertical scan frequency is applied thereto. An impedance winding is affixed to the center leg of the saturable reactor and a sawtooth-shaped potential at the horizontal scan frequency is applied thereto. This horizontal scan signal is modulated at the vertical scan rate to provide the desired side pin-cushion correction signals.
Although the above-mentioned "E" core type saturable reactor having equal air gaps in all of the leg members has proved satisfactory for effecting side pin-cushion correction in numerous applications, it has been found that there are other applications wherein such apparatus appears to be less than adequate. More specifically, it has been found that display systems which require alterations in deflection yoke configuration wherein the inductance of the yoke is altered with respect to the inductance of the "E" core saturable reactor no longer effect satisfactory side pin-cushion correction.
For example, it has been found that deflection systems having a 110.degree. deflection angle require a deflection yoke of altered characteristics to effect the desired increase in deflection angle. However, the altered deflection yoke in combination with the above-mentioned "E" core saturable reactor tends to provide an inductance level in excess of the desired maximum and minimum levels. Although the overall inductance level can be reduced to the desired level by increasing the magnitude of the air gaps, it has been found that the increased air gap magnitude causes an undesired reduction in the amount of change of inductance effected by the control winding whereupon the desired side pin-cushion correction is no longer correctly effected.
While "E" core type saturable reactors with three leg members each having an equal gap have been satisfactory for deflection systems with a deflection angle of up to about 90.degree., it has been found that there are other applications, such as 110.degree. deflection systems, wherein such apparatus does not appear to be quite adequate. For example, it has been found that a change in the inductance ratio of the yoke and saturable reactor has a deleterious effect upon the above-mentioned side pin-cushion correction. Moreover, a shift in such features as deflection angles, yoke structure such as "saddle to torroid," or cathode ray tube structure tend to accentuate the undesired shift in inductance ratios.